8th International Nannoplankton Association Conference


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Laurel M. Bybell, Thomas G. Gibson:
Calcareous nannofossils associated with the Late Paleocene thermal maximum event in New Jersey

Two cores from the coastal plain of New Jersey (Gloucester County) have unusually complete marine sections associated with the Late Paleocene Thermal Maximum (LPTM), a global event that occurred within the uppermost part of Calcareous Nannofossil Zone NP9 and contains a significant carbon isotope excursion (CIE). Both the Clayton core and the Wilson Lake core contain approximately 15' (4.6m) of sediments between the base of the LPTM/CIE and the base of Zone NP10. A detailed investigation of these sediments revealed that several calcareous nannofossil events occurred within 2' (0.6m) of the LPTM/CIE: the first appearance datum (FAD) of both Transversopontis pulcher and Toweius occultatus, the last appearance datum (LAD) of Fasciculithus alanii, and a sudden drop in abundance of Toweius eminens eminens, Toweius eminens tovae, Scapholithus apertus, Fasciculithus schaubii and Chiasmolithus bidens, with only occasional specimens of these species occurring above the event. If the LPTM/CIE is designated as the Paleocene/Eocene boundary, the FAD of T. pulcher is the most suitable calcareous nannofossil species for indicating proximity to the boundary.

There has been uncertainty concerning the FAD of the genus Rhomboaster in relation to the LPTM/CIE. In the Clayton core, the first member of this genus to appear is Rhomboaster spineus, which has its FAD 11' (3.4m) above the base of the LPTM and 3.5' (1.1m) below the FAD of Rhomboaster bramlettei (base Zone NP10). In the Wilson Lake core, R. spineus again is the first representative of this genus to appear, and its FAD is 12' (3.7m) above the base of the LPTM/CIE and 3' (0.9m) below the FAD of R. bramlettei. In both of these sections, the genus Rhomboaster definitely first occurs well above the base of the LPTM/CIE. Few locations elsewhere have as complete a LPTM/CIE section as found in the Clayton and Wilson Lake cores. One exception is DSDP Site 690, in the Southern Ocean, where the first Rhomboaster also occurs well above the base of the LPTM/CIE. Even downdip sections at Island Beach, New Jersey and DSDP Site 605 off New Jersey have an unconformable interval at this event, and sediments of Zone NP10 age rest directly upon pre-LPTM/CIE sediments. Thus, it seems possible that reported occurrences of Rhomboaster coincident with the LPTM/CIE reflect missing section and are indicative of hiatuses. The occasional Rhomboaster reported below the LPTM/CIE is more problematical but may well result from burrowing or from mixing of sediments during formation of erosional unconformities.


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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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